Flat panel display devices are widely used as those for personal computers, handy information processing equipment, television receivers, etc. Recently, display devices using light-emitting elements such as organic EL (electro-luminescence) elements have attracted considerable attention and have been actively researched and developed. Organic EL display devices have the following features: (1) they do not need a rear light source that would prevent them from being made thin in thickness and light in weight, (2) they are suitable for the reproduction of moving images because of a rapid response characteristic, and (3) they can be used in cold locations because their brightness remains substantially unchanged in low temperatures.
The organic EL display devices are provided with display elements disposed in a matrix form to emit red, blue and green light. The display element consists of an anode, a cathode and a light-emitting layer. Materials for the light-emitting layer each are selected in accordance with wave lengths of the colors to be emitted.
It is necessary to drive each color in the organic EL display device in response to its light-emitting characteristics. It is known that a color can be driven by using different reference gray scale signals to match with the light emitting characteristics. Usually, a reference gray scale signal circuit is provided exclusively for every color to supply an output signal to its corresponding digital-to-analog conversion circuit.
In the display device video signals are generally written successively on a time-sharing basis for a horizontal display period. In order to carry it out successfully, the driving method has limitations with respect to display panel size, the number of pixels, integrated circuit (IC) performance, etc.